A disk drive is a data storage device that stores data in concentric tracks on a disk. Data is written to or read from the disk by spinning the disk about a central axis while positioning a transducer near a target track of the disk. During a read operation, data is transferred from the target track to an attached host through the transducer. During a write operation, data is transferred in the opposite direction.
During typical disk drive operation, the transducer does not contact the surface of the disk. Instead, the transducer rides along a cushion of air generated by the motion of the disk. The transducer is normally mounted within a slider structure that provides the necessary lift in response to the air currents generated by the disk. The distance between the transducer/slider and the disk surface during disk drive operation is known as the “fly height” of the transducer.
Because the transducer is held aloft during disk drive operation, friction and wear problems associated with contact between the transducer and the disk surface are usually avoided. However, due to the extremely close spacing of the heads and disk surface, minor variations in the read-write heads or disk platters can lead to a head crash—a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film. For giant magnetoresistive head technologies (GMR heads) in particular, a minor head contact (that does not remove the magnetic surface of the disk) could still result in the head temporarily overheating, due to friction with the disk surface, and renders the disk unreadable until the head temperature stabilizes.
The detection of the exact point of head disk contact is critical in disk drives since such contact could also lead to permanent damage to the recording head and/or the disk media. It is even more so for newer recording heads with the Dynamic Fly Height (DFH) technology. Such a recording head has an embedded heater in close proximity to the recording element. Localized thermal expansion when the heater is powered allows the fly height of the transducer be adjusted, thus achieving higher recording density. In order to properly calibrate the drive and heater, head/disk contact is needed at least once. It may also be desirable to recalibrated the drive at specified intervals during disk usage.
What is needed is a system to detect head disk contact upon initial calibration or re-calibration of the disk drive and the parameters that cause such contact. Once these parameters are determined, they can be monitored during disk operation to ensure any subsequent head disk contact does not occur.